Manufacture of tetraethyllead



y 7, 3 c. M. NEHER ETAL 2,644,827

MANUFACTURE OF TE'I'RAETHYLLEAD.

164 Aug. 31, 1951 INVENTORS CLARENCE M. NEHER FRANK L. PADGITT BY PAUL E. WEIMER Patented July 7, 1953 2,644,827 MANUFACTURE OF TETRAETHYLLEAD Clarence M. Neher, Frank L. Padgitt, and Paul E. Weimer, Baton Rouge, La.., assignors to EthylCorporation, New York,

tion of Delaware N. Y., a. corpora- Application August 31, 1951, Serial No. 244,514

This invention relates to the manufacture of tetraethyllead. Morep'articularly, the invention relates to a new and improved process whereby 6 Claims. (01. 260-437) tetraethyllead is manufactured by the ethylation of an active formof lead in a continuous manner.

Tetraethyllead may be synthesized by a num' ber of reactions, a preferred procedure involving the ethylation'of an alloy of lead and an alkali metal at'elevatedtemperature with anethylating agent. Typical'of such operations is the ethylathat it is a batch operation and therefore sub-- ject to all the usual limitations of a batch operas 1 tion.

tion of lead monosodium alloy with ethyl chloride, according to the equation; I H

4NaPb+4C2HsCl Pb (c2115) 4+4NaCl+3Pb The commercial process according to this reaction has consistently been carried out in batch-operations. In such techniques, a quantity of sodiumlead alloy, NaPb, is charged to an autoclave, the alloy being in the form ,of commin'uted granular solids. Heating and agitation of the autoclave contents is then started and ethyl chloride liquid feed is introduced. The ethyl chloride ,and alloy start reacting with increase in temperature,

thereby increasing the pressure inside the reactor.

The pressure is controlled by the rate of feed of the ethyl chloride. Upon completion of the ethyl chloride feed, the autoclave cha'rgeis maintained at the elevated temperature and'pressure for fur]- ther reaction.v Excess ethyl chloride is then vaporized from the autoclave charge, the vaporization being facilitated by circulation of heating medium through a jacket on the autoclave.

The contents of theautoclave on completion of the cycle is a dry, powdered mass termed reaction mass, containingexcess metallic lead, tetraethyllead,

the tetraethyllead i steam distilledwhile the still charge is vigorously agitated' According to the above method, the ethyl chloride is fed 7 in the ratio of about one-half part 35, and sodium chloride, and minor amounts of sodium or sodium-lead alloy. The reaction mass is discharged to a steam still, wherein it is first immersed in water and then by weight to one part of sodium-lead alloy. As

already described, such a ratio of reactants, upon dered mass. In the couse of the above described completion of the reaction, produces a dry, powi I that the solids do not impinge on eachother with steam distillation recovery method, frequent difficulty is encountered owing to agglomeration of the solid particles, which are predominantly lead. Such agglomeration tends to deposit lead sheets on the steam still, or to form balls or other massive forms of lead, which wedge the agitator'and I consequently interrupt the recovery operation.

The foregoing interruptions to the recovery op"-' eration is of course a deficiency of the former process. In addition, the process has been hampered by other deficiencies which have 'longbeen' recognized and studied but not solved. A major disadvantage of the prior process 'lies'in'the fact Such disadvantages include the thermal inefiiciency arising from the cyclic variations in the temperature of the equipment. In addition, batch operations are notorious in requiring moreoperating labor than a continuous 'flow process. Furthermore, in batch operationsonly a relatively minor fraction of the totaltime cycle is devoted to the actual reaction, a large percentage of the time being needed for charging, discharging, and the purification step of vaporizing excess ethyl chloride from the autoclave charge.

An object of the presentinvention is to provide a new and improved process capable of eflicient continuous operation in the manufacture of tetraethyllead. Another important object is to assure high yields of tetraethyllead. An additional object is to'virtually negate the possibilityiof de composition of the tetraethyllead in the ethylation zone, and also to provide an ethylatedmixture particularly susceptible to efficient recovery of the tetraethyllead therefrom. Yet another object is to provide a high production rate in terms of tetraethyllead produced per unit volume of reaction space.

Broadly defined, the invention comprises the ethylation of the lead of an alloy of lead and an alkali metal with a liquid ethylating agent, in the presence of a substantial excess of the ethylating agent. The mitxure of components, or ethyla tion mixture, is stirred or agitated under nonideal conditions; that is, the agitation is appr'e c'iably short of that required to provide uniform or ideal distribution of solids throughout theethylation mixture. -Although the solids in the ethylation zone are non-uniformlydistributed, nevertheless a high fraction of about percent or more are suspended by virtue of the agitation and'all solids are in vigorous motion. In other words, the liquid proportions at all points is such of lead which is a large component cfthe ethylation mixture solids.

Although the solids present are maintained in the described non-uniform state of distribution,

gree of ethylation, but at the same time the tetraethyllead product is uniformly distributed through the predominantly ethyl chloride liquid phase. Surprisingly, the liquid phase does not show a composition gradient even when the lead containing alloy is fed cyclically. By cyclically is meant that the ethylation is carried out continuously but the alloy is fed intermittently in.

batches for greater convenience. Even under such conditions, we are unable to detect a stratification of the liquid phase in terms of the tetraethyllead content.

The advantages and best method of operating the process are more easily understood from the following description and example and the accompanying figure. The figure is a diagrammatic representation of apparatus for a preferred and easily operable embodiment of the process.

Referring to the figure, the principal unit of apparatus is the ethylation vessel or ethylator l.

The usual auxiliary equipment includes an ethyl chloride supply tank 2 and feed line 3, and an alloy supply hopper '4 fitted with lines 43, M, for maintaining an inert gas atmosphere in contact with the alloy. A feed column 5, which can be blocked off by valves 6,1, provides a pressurized feed chamber from which the-comminuted alloy can be dropped into the feedend of conveyer 8. Provision is made for pressure blanketing of the alloy in feed chamber 5 by inert gas lines 45, 4B. A drive motor 9 powers the conveyer, which transports the alloy into the ethylator I at the top, that is into a vapor space. The ethyl chloride feed rate through line 3 is controlled by valve 10, a flow meter ll providing visual check on the rate of flow.

The ethylated mixture from the ethylator isdischarged through one or more nozzles and valves of the outlet manifold assembly l2. Thus nozzle line I32 can be used for the discharge by opening valve I42. The discharged stream, re-

gardless of which nozzle or tap it is released through, is passed through line [5, to a solidsliquid separator IS. A bottom discharge line I! discharges solids, which include lead metal and alkali metal chlorides, to subsequent operations Removal of the 1 for the recoveryofmetal values. liquid phase from the solids-liquid separator "is accomplished through line IS, the flow rate to the tetraethyllead concentration apparatus l9 being;

controlled by valve 20. The concentration unit I9 may take several different forms, a preferred- Agitation elements within the ethylator inthe ethylator through line 42 for cleanout.

clude the propeller type agitators 29, 30, 3|, and the bottom plate element 32, all these elements being mounted on shaft 33, driven by motor 34. This agitator assembly in operating stirs the mixture in the ethylator, including the alloy and reaction products, and the liquid phase. A vapor blow off line 36 from the ethylatonprovides for release of vapor when a decrease in pressure is necessary, either through pressure release line 31 and valve 38, or through the manually operated valve 39.

A bottom'discharge valve 4| allows draining During operation, the level of the ethylation mixture is asce'rtainablefrom a liquid level gauge 40.

Wide variability in apparatus is possible, the process not being confined to any specific ethylation vessel. Thus, in large capacity installations it will be advantageous to use a plurality of agitating assemblies, each of relatively small sweep area in comparison with the cross sectional area of the'ethylator. In such instances, the same results will be obtained and the process will benefit in that reliance is not placed on only one drive motor, as in the typical apparatus described above.

As'the process is-not limited to a particular form or composition of lead alloy, various alternatives to the feed equipment are available.

' Thus, instead of the feed equipment forsolid comminuted alloy in the figure, an alternative arrangement can be easily substituted for feeding the alloy in the liquid or molten phase. In such case, the alloy feed apparatus will consist simply of a. molten alloy supply tank and a feed line and nozzle for passing the liquid alloy to the ethylation zone.

The solids-liquid separator 16 may utilize any of several different unit operations. Thus, the ethylated slurry is susceptible of filtration, so that the solids-liquid separator can be a continuous filter of types available. Alternatively, it has also been discovered that ethylated mixtures can be resolved into a solids stream virtually free of tetraethyllead by lixiviation with a solvent, such as naphtha, benzene, or preferably, an alkyl chloride. Ethyl chloride itself is a highly effective solvent for the tetraethyllead. Accordingly, the solids-liquid separator can be an extraction operation in which the liquid phase is dissolved in ethyl chloride and separated from the solids with high efliciency.

The advantages and benefits of the process as well as the mode of operation are illustrated by the following workingexample. In the example, all flows and compositions are in parts or percentages by weight, except as, otherwise specified.

Example The ethylator I was charged with ethyl chloride through line I0. Hot water was circulated to the jacket 23 through line 24 until the charge was at a temperature of C. Monosodiumlead alloy, in the form of thin flakes, which had been'previously charged to the alloy feed column 5 was then charged by opening valve 1 and operating feed conveyer 8. Agitation of the charge wasstarted immediately before alloy fiow was started, the speed of rotation providing a peripheral velocity of 660 feet per minute.

Steady operation was soon achieved, the ethylator being discharged through a draw of! line located approximately at the midpoint, that isSSpercent of the total depth of the ethylation mixture above the bottom point thereof. The

ethyl chloride and sodium-lead alloy were fed at the weight ration of 5.0:1.0, ethyl chlorideralloy, corresponding to an excess of approximately 1700 percent of the ethyl chloride theoretically required. The volumetric feed rates in'terms of pounds per hour per cubic foot of ethylation zone, amounted to 6.5 pounds of sodium-lead alloy.

' Steady conditions were maintained for an extended period. The slurry withdrawn from the ethylator, by a series of analyses, hadthe following compositon:

Weight percent Tetraethyllead 5.5 Ethyl chloride 19.0 Sodium chloride 4.0- Lead 1'1.0-fr- Sodium (as NaPb) 0.5

In-this-operation, a residence time of 110 mint utes was maintained, the ethylation mixture being at the temperature of 85 C. and a pressure of 110 pounds per square inch gauge throughout the operation. Power input to the agitator 33 was slightly less than 0.1 horsepower per cubic foot of ethylation mixture. The tetraethyllead was produced at the volumetric production rate of 2.15 pounds, a yield of 93.7 percent being obtained.

The ease of operation and high yields obtained by the process are evident from the foregoing example. In this specific run, the yield of 93.7

percent is about 5 percent higher than the yields in thousands of commerical batch ethylations. In numerous other runs by the present process similar yield improvements, of the order of several percent have been found on the basis of analysis of both liquid phase and total slurry samples. A satisfactory degree of reproducibility was shown by statistical treatment of the results.

The reason for the high yields obtained in the process are not fully understood, but aplausible theory has been developed on the basis of careful observation of numerous operations. Without intending the process to be limited by any theory as to the improvements effected, it yet appears that the formation of tetraethyllead is a stagewise chemical reaction. Apparently an intermediate complex of undefined composition is first formed, which is capable of further re-. action to give either tetraethyllead, or alternatively, by-products which include and are evidenced by evolution of gaseous compounds. These gaseous compounds include methane, ethane, ethylene and butanes. Material balances on a series of ethylation's by the present process showed that the amount of such byproducts were reduced approximately 40 percent from the amount accompanying the conventional commercial ethylationprocedure. Inasmuch as it has been shown that by-product formation is evidence of diversion of a proportionate amount of alkali metal from the desired formation of tetraethyllead, it is apparent that by the present invention, loss of alkali metal in 'byproduct formation is reduced. It is therefore believed that the high yields of the process are a result of the uniform temperature at all pointsin the ethylation zone, and the uniform composition of the liquid phase. owing j to the preponderance of solids in the ethylation mixture there was little or noopportunity for the liquid reaction products, including the tetraethyllead formed, to be removed or distributed away from the immediate locale of for-.

mation. As a result hot spots were frequently formed within theg ethylation mixture which could result in either partial decomposition of tetraethyllead, or else diversion of theprobable.

intermediate to by-product formation. In contrast, in the present process, the localized high concentrations of either tetraethyllead or intermediates are minimized and in additon a uniform temperature is maintained throughout the system.

A particular virtue of the process is that the residence time of the solid components of the ethylation mixture can be controlled at will and to some extent independently of the feed ratioof the ethylating liquid and the solids. The significance of this findingis that, for example, if

a particularly thin product slurry is desired. nevertheless the ethylation mixture can be main-- tained with an appreciably high solids content and the. benefits of an extended residence time attained. Thus, in operation according to the foregoing example, but withdrawing at the top of the ethylation mixture, a liquid solid ratio of 2:1-

is achieved within the ethylator. For the same feed rates as in the above example, then, an average residence time of about minutes canfall below a liquid': solid weight ratio of 3:1

within the ethylation mixture. Theupper-limit of the preferred range is a liquid solid'ratio of 5:1. Operation below this range, in conjunction with the non-ideal agitation which is a characteristic of the process, results in mechanie cal attrition of the solids'p'articles, which, being largely metallic lead, are susceptible to mechanical fusion to form masses which can bind the agitator operation.

i As already stated, non-ideal agitation of the ethylation mixture is an essential characteristic of the process. On the other hand, sufficient agitation powerinput, efiicientlyusedis requiredto maintain all the solids present discretely dispersed in the liquid phase. By efficient agitation is meantthat the mechanical horsepower input of the agitator assembly is distributed to various strata in the'ethylation zone according to methods frequently used. Among the factors which sweep of rotating agitator elements, and the nearness of the lowest agitating element to the bottom of the ethylation zone. Satisfactory agitation can be achieved with agitation sweep area varying 'fromabout 10 to about 60 percent of the ethylation zone cross sectional area. In general, it is preferred to'use agitating elements, which can be either propellers or turbine agitators, which sweep at least 40 percent of the ethylation zone cross sectional area. The lower ranges are avoided as higher radial speeds are- In prior ethylations,

required for a given mechanical horsepower input, which in turn increases the mechanical loss at the sealing or entrance point for the agitator assembly.

With respect to the vertical position of the agitation elements, it has been found that in virtually all instances the lowermost element should be appreciably closer to the bottom of the ethylation zone than is common practice. Thus, frequently the lowermost turbine or propeller is within a distance of from one-fourth to one-half of its diameter to the bottom of the zone.

In most embodiments of the process, a total depth of ethylation mixture of at least several feet, and up to about four feet, will be employed. To assure distribution of some solids throughout this ethylation zone, a plurality of agitating elements is customarily provided. A desirable vertical disposition of such plural elements is at space intervals of about one-half to threefourths of the diameter of such elements.

The power requirements of the process will of course depend to some extent on the mechanical losses in the drive mechanism and similar mechanical devices, such as the gland or seal at which. the agitator shaft enters the enclosed ethylation zone. Measurement of such losses, however, has shown the actual horsepower requirements to the agitator shaft. Surprisingly, the minimum horsepower requirements did not vary with a reduction in liquid solid ratio in the range of 4:1 to 2:1, but satisfactory agitation was achieved with a power input of approximately 0.1 horsepower per cubic foot of ethylation zone. As a general rule, power inputs of over 0.5 horsepower per cubic foot are avoided in order to assure the non-uniform distribution of solids essential to the process.

As mentioned above, a significant feature of the process is the control of the residence time of the solids within the ethylation zone. This is achieved by the removal or discharge of a product slurry at a point remote from the bottom of the ethylation vessel, which in turn takes advantage of the effects of the non-ideal agitation employed. It has been found that by non-uniform distribution of the solids, a segregation both in terms of weight concentration and in terms of chemical composition is attained.

As an example of the gradation of chemical composition of the solids, slurry samples were removed from an ethylator operated similarly to that described in the working example. The samples were removed at the bottom and at the midpoint, that is, at a point corresponding to 50 percent of the total depth of the ethylation mixture. The liquid solid ratios at the bottom and midpoint were 1.6:1 and 4.9:1, respectively. Analyses of the solids in these samples also showed that the ethylation was only '79 percent complete at this point but was 8'7 percent complete at the midpoint. The solids in the product slurry contained a lower proportion of unreacted solids than either of the foregoing samples.

It is apparent from the foregoing that appropriate selection of the withdrawal point allows retention of the reacting materials within the ethylation zone until the desired degree of ethylation is attained. In general, it is preferred to discharge at or above the midpoint of the ethylation zone. For the maximum residence time an overflow discharge is used. An overflow discharge, however, requires a feed ratio of liquid solid of the order of :1 or greater if the ratio within the ethylator is not to drop below the 8 preferred range of 3:1. For this reason a discharge point between the midpoint and the overflow level is frequently employed.

The process has thus far been primarily described with reference only to use of a single ethylator. The principles of the process are nevertheless applicable in multi-stage operations and the same benefits will be realized. In every case, the charge in a specific individual ethylation zone is agitated in a non-ideal fashion. Accordingly, in each stage the withdrawal of a discharge slurry at a point remote from the bottom utilizes such non-ideal agitation to segregate the solids within the ethylator according to the degree of ethylation.

The process is not limited to a specific ethylation reaction, but is applicable to ethylation reactions involving sodium-lead alloys of relatively high sodium content. For example, the process is applicable in the ethylation of alloys of the composition corresponding to the formula NazPb, or with lesser and greater proportions of sodium. In addition, alloys with other alkali metal comonents are suitable feed components and similar benefits will be realized. For example alloys containing potassium, either as the sole alkali metal, or as a component of a ternary alloy, can be advantageously ethylated by the process.

Although ethyl chloride is the preferred ethylating agent, other ethylating agents may be substituted for the ethyl chloride and the benefits of the method will be realized, although in varying degree. Examples of alternative ethylating agents which can thus be substituted for the ethyl chloride are ethyl bromide, ethyl iodide, and diethyl sulfate. As a practical matter, ethyl chloride will be most widely used owing to the cheapness and availability of this chemical.

The foregoing description of the process illustrates the effectiveness with which the objects of the invention are attained. Having fully described the invention and the best manner in which it is carried out, what we claim is:

l. The continuous process of making tetraethyllead comprising feeding an alkali metal alloy of lead and a liquid ethylating agent to an ethylation zone, in the proportions of at least 2 parts by weight of ethylating agent to 1 part by weight of alloy, and ethylating therein, agitating the ethylation mixture only sufficiently to maintain the reacting and reacted solids in non-uniform distribution in a liquid comprising a solution of tetraethyllead in the ethylating agent, said liquid being of uniform composition throughout the ethylation zone. and withdrawing at a point remote from the bottom of the ethylation zone a slurry of solids in the liquid, said solids being more ethylated than the solids in the ethylation zone.

2. The continuous process of making tetraethyllead comprising feeding ethyl chloride and monosodium-lead alloy to an ethylation zone in proportions of at least 2 parts by weight of ethyl chloride to 1 part by weight of alloy, ethylating therein while agitating only sufiiciently to maintain the reacting and reacted solids in non-uniform distribution in a liquid of uniform composition throughout the ethylation zone, the liquid comprising a solution of tetraethyllead in ethyl chloride, and withdrawing at a point remote from the bottom of the ethylation zone a slurry of solids in the liquid, the solids being higher in reacted solids content than the solids in the ethylation zone.

3. The continuous process of making tetraethyllead comprising feeding ethyl chloride and monosodium-lead alloy to an ethylation zone in the proportions of at least 2 parts by Weight of ethyl chloride to 1 part by weight of alloy, ethylating therein while agitating only sufficiently to maintain the reacting and reacted solids in nonuniform distribution in a liquid of uniform composition throughout the ethylation zone, the liquid comprising a solution of tetraethyllead in ethyl chloride, and withdrawing at a point in the upper 50 percent of the total depth of the ethylation zone a slurry of solids in the liquid, the solids being higher in reacted solids content than the average solids in the ethylation zone, the withdrawal point providing a liquid to solids weight ratio within the ethylation zone of at least 3:1.

4. The process of claim 2 further defined in that the monosodium-lead alloy is fed while in the molten state.

5. The process of claim 2 further defined in that the monosodium-lead alloy is fed in the form of comminuted solids,

6. In the process of ethylating lead by contacting particles of an alkali metal alloy of lead with a liquid ethylating agent, the improvement which comprises efiecting the contacting in a I in said liquid, agitating the reaction mixture suf- 10 tank in which the reactants are proportioned with a large excess of liquid to keep the reaction mixture in the form of a slurry of solid particles ficiently vigorously to cause the liquid to be sub stantially uniform in composition throughout, but not vigorously enough to cause all the solid particles to be uniformly distributed so that the less reacted particles are stratified under the action of gravity below the more reacted particles, and removing reaction products by making withdrawals of both solid and liquid from the upper portion of the reaction mixture.

CLARENCE M. NEHER. FRANK L. PADGIT'I. PAUL E. WEIMER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,091,114 Davot Aug. 24, 1937 FOREIGN PATENTS Number Country Date 963,005 France June 27, 1950 

1. THE CONTINUOUS PROCESS OF MAKING TETRAETHYLLEAD COMPRISING FEEDING AN ALKALI METAL ALLOY OF LEAD AND A LIQUID ETHYLATING AGENT TO AN ETHYLATION ZONE, IN THE PROPORTIONS OF AT LEAST 2 PARTS BY WEIGHT OF ETHLATING AGENT TO 1 PARTY BY WEIGHT OF ALLOY, AND ETHYLATING THEREIN, AGITATING THE ETHYLATION MIXTURE ONLY SUFFICIENTLY TO MAINTAIN THE REACTING AND REACTED SOLIDS IN NON-UNIFORM DISTRIBUTION IN A LIQUID COMPRISING A SOLUTION OF TETRAETHYLLEAD IN THE ETHYLATING AGENT, SAID LIQUID BEING OF UNIFORM COMPOSITION THROUGHOUT THE ETHYLATION ZONE, AND WITHDRAWING AT A POINT REMOTE FROM THE BOTTOM OF THE ETHYLATION ZONE A SLURRY OF SOLIDS IN THE LIQUID, SAID SOLIDS BEING MORE ETHYLATED THAN THE SOLIDS IN THE ETHYLATION ZONE. 